Lens system



May 16, 1939- w. SCHADE 2,158,202

LENS SYSTEM Filed Nov. 19, 1937 Patented May 16, 1939 UNITED STATES PATENT OFFICE 6 Claims. (Cl. 88-57) This invention relates to lens systems and particularly to image forming lens systems such as are used in photography.

More specically it relates to image forming claim one particular arrangement in a copending application Serial No. 175,474, tiled concurrently herewith.

Other objects and advantages of the present systems of high magnication, i. e. systems which invention will be apparent from the following 5 are particularly useful when employed to have description when read in connection with the conjugate images vastly diierent in size. In phoaccompanying drawing showing a preferred emtography or cinematography the image on the bodixnent thereof. lm is usually many times smaller than the origi- The lens system shown in cross section in the 10 nal subject. In lantern slide or cinematographic accompanying drawing has the following speci- 10 projection, the image on the screen is many times tlcations which correspond to the table accomlarger than that on the slide or film. panying the drawing. 1'/ 1.3 F=100 min.

It is an object of the invention to provide an objective particularly suitable for projection purposes or when reversed, for photographic pur- Lens Glass Rad Spacing 15 poses.- For convenience, I include all such lenses D l' 5224 Mm Mm. under the self-explanatory term "high magnii izo-+Qu iication image forming systems. 59' R, 75 1 "M As a high magniilcation image forming lens, No1-imi o-us 2o it is common practice to use a Petzval type lens H ao R"m 20 consisting of two widely spaced achromats, the rio-7e3 one on the long focus side usually being a cem {NW1-5163 RFM, 3 mented doublet and the one on the short focus ,-oio :pito side being either a cemented or a spaced doublet. R"65 o o It is an object oi the present invention to 1.5750 25 provide a modied Petzval lens system more IV 42.7 R"+ highly corrected than hitherto. The system prosl-:mt vided thereby is highly corrected over a. wide iield v {ND-1' m3 R1 +85 0 1M and is capable of working satisfactorily at an ,-64.0

3o aperture of about f. 1.3 whereas previously pro- RFA :FM4 30 posed modifications have reached only f. 1.5 or N11-1.5750 f. 1.6' VI 427 l SI-z-G (back OGUS) With certain minor exceptions, a Petzval type R.- -sooo lens system is one having two widely spaced achromatic components. The invention is not Fiollowlng Petzval,s teachings thls lons ls made 35 particularly concerned with the one on the long up of two widely spaced aohromatlo componen locus side which may be a. simple doublet or The space (S1) ls shown as about 75 per com of if desired may be modiiled to follow any suitthe focal length of the system In the above able Prior teachings Wh regard to this Compo mentioned copending application, the modied 40 nent. According to the invention, the other com- Petzval lens shown has a spacing between the 4o ponent, however, is specifically arranged to have Components which is only slightly greater than its stronger curvatures convex toward the short one quarter of the focal length of the system. focus side of the objective and preferably con- Thus a Petzval type lens may be dened as one sists of a plurality oi.' cemented doublets (two having two achromats spaced by more than one being SufCent fOI mOSt purposes) in each 0f quarter of the focal length or in the more usual 45 which the cemented surface is the strongest one casos more than one half of the foosl length. and is convex to the short focus side, i. e. con- Petzval lenses have also been proposed 1n which cave to the other component. The components the Components ere not separaten? fully somoon the long and the short focus sides are usually metized-one component being over corrected to called the front and rear components respeccompensate for the other, Such variations may 50 tively, but the light enters the system from oppobe incorporated with the present invention withsite sides depending pn Whether it is used for out departing from the spirit thereof. According taking O1' Projection DUIDOSBS- to the invention, the rear component is made up In connection with the various front compoof two cemented doublets, elements HI, IV, V nents which maybeused herewith, I describe and and VI, the cemented surfaces (Rs and Ra) of 55 which are convex to the short focus side of objective and in each case are stronger than the outer surfaces of the doublet.

The plurality of doublets making up the rear component may be identical for economy in manufacture, if desired, but in the preferred arrangement shown, they are not identical.

I have found that a lens made up according to my invention retains all of the good characteristics of the Petzval type lens, namely, good correction for spherical aberration and coma; in fact, it even improves these factors somewhat. In addition, there is a very considerable reduction of the curvature of eld and astigmatism, partly due to the reduced Petzval sum. It will be understood that the invention is not limited to the specific structure shown, but is of the scope of the appended claims.

What I claim and desire to secure by Letters Patent of the United States is:

1. An image forming objective comprising an achromatic front component and an achromatic rear component spaced therefrom more than one quarter of and less than twice the focal length of the objective, said rear component consisting of two doublets each having a cemented surface concave to the front component and With a radius of curvature less than its outer surfaces and greater than one quarter of the focal length of the objective.

2. A high aperture, high magnification, image forming objective having as a. component on the long focus side an achromat and a second achromatic component spaced therefrom about threefourths of the focal length of the objective, said second component comprising two separate doublets the cemented surfaces of which are convex to the short focus side of the objective and the rear surfaces of which have radii of curvature greater than the respective cemented surfaces.

3. A lens for projecting lantern slides comprising an achromatic front component and an achromatic rear component spaced more than quarter the focal length of the lens from the front component and between said front component and the plane for the lantern slide, said rear component consisting of two separate doublets each having its cemented surface convex to said lantern slide plane.

4. A Petzval type of lens having an achromatic front component and an achromatic rear com# ponent consisting of a plurality of doublets in which the cemented surfaces are concave to the front component and have stronger curvatures than the outer surfaces.

5. A Petzval type lens having front and rear components separately corrected for color and together fully corrected for at least two colors to form an achromatic system, the rear component consisting of a plurality of doublets in which the cemented surfaces are concave to the front component and have stronger curvatures than the outer surfaces.

6. An objective of the Petzval type, in which the rear component consists of two doublets with their cemented surfaces concave to the front component.

WILLY SCHADE. 

